Optical evidence of a pseudogap in the ferromagnetic metallic phase of the bilayered manganite

Abstract Low-energy (0.5–4 meV) charge dynamics have been investigated for a -axis-oriented thin films of the bilayered perovskite-type manganite La 2−2 x Sr 1+2 x Mn 2 O 7 ( x =0.3) by using THz time-domain spectroscopy. In the ferromagnetic metallic phase, we observed a clear gap signature, while the film exhibits paramagnetic insulator to ferromagnetic metal transition at 250 K according to the resistivity and magnetization measurements. This provides the evidence of a pseudogap in the ferromagnetic phase of La 2−2 x Sr 1+2 x Mn 2 O 7 ( x =0.3).